For the operation of electrical consumers, which are also designated as loads, on-board power systems are provided in motor vehicles. Some types of consumers are particularly sensitive to voltage dips or voltage spikes in the supply voltage, for example on-board power system electronics or even the lighting. If such sensitive consumers are subjected to a voltage dip or a voltage spike, then their function can be at least partly impaired. In this case, the operation of the vehicle can be impaired and/or undesirable side effects such as momentary darkening of the lighting of the motor vehicle arise.
It is furthermore known to use rechargeable batteries having low internal resistance and high electrical power to absorb voltage spikes or voltage dips. However, significant voltage dips arise particularly in the case of high, abrupt loadings despite high capacities and powers (and despite high space requirement associated therewith and high weight).
Furthermore, particularly in modern vehicles, dynamic electrical consumers are present, the operation of which can cause a severe voltage dip, for instance a starter motor of a start/stop module or a drive of an electrical steering system, such as are used in parking assistants. These dynamic consumers, in particular, are also activated during the operation of the vehicle and not just upon the initial cold start or when parking the vehicle.
Since operation is intended to be ensured between the initial cold start and the final parking of the vehicle, the document DE 10248658 B4, for example, proposes, for on-board power system stabilization of a vehicle having a start/stop module, providing a further energy store besides the customary on-board power system rechargeable battery, said further energy store being used for backup in the event of a voltage dip. According to said document, a changeover switch (not described in greater detail) switches between the customary lead-acid rechargeable battery and the second energy store, a voltage spike that arises as a result of the changeover being absorbed by a power distributor. The power distributor is based on a pulse-width-modulated power switch. Furthermore, the second energy store is operated by a DC/DC voltage converter, such that the overall outlay on power components for on-board power system stabilization is high. The solution proposed in said document is therefore associated with high costs. Furthermore, said document does not reveal any indication of a safety mechanism in the case of a fault in the changeover switch, such that the circuit described therein, in the event of faulty behavior of the changeover switch, can lead to the destruction of components of the circuit, in particular to the overcharging of the second energy store, which, when realized as a super capacitor, can rupture in the event of overcharging.